Презентация "Amplitude modulation"

Amplitude modulation

Completed: Ichetovkin Artem

Amplitude modulation  ( AM ) is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave.

Contents:

• Applications in radio engineering
• Formula
• Bibliography

Applications in radio engineering

The first experiments on the transmission of speech and music using radio waves by amplitude modulation were carried out in 1906 by the American engineer R. Fessenden. In his experiments, the carrier frequency of 50 kHz of the radio transmitter was generated by an electric machine generator (alternator), for its modulation a microphone was added between the generator and the antenna, changing the attenuation of the signal in the circuit.

Since 1920, instead of electromachine generators for the generation of carrier frequency, generators for electron tubes have been used. In the second half of the 1930s, as far as the development of ultrashort waves, amplitude modulation gradually began to be displaced from radio broadcasting and radio communication by VHF frequency modulation.

Since the middle of the twentieth century, in the service and amateur radio communications, on all frequencies, modulation with one sideband (OWP) has started, which has a number of important advantages over AM, the main one of which is a 2-fold narrowing of the frequency band occupied by the radio signal. In connection with this, it was proposed to transfer to mass-media and mass broadcasting, but this would require replacing all broadcasting receivers with more complex and expensive ones, so this was not done.

At the end of the 20th century, the transition to digital broadcasting began using signals with amplitude manipulation.

An audio signal (top) may be carried by a carrier signal using AM or FM methods.

Formula

Let

• ,
• The carrier (simulated) signal (carrier wave).

Then the amplitude-modulated signal

has the form :

(1)

Here  m  — a certain non-negative constant, called the modulation coefficient. Formula (1) describes a carrier signal  , amplitude modulated signal

  with a modulation factor   m .

For undistorted modulation, the condition  . The fulfillment of this condition is necessary in order for the expression in square brackets in (1) has always been positive. If it can take negative values at some point in time, then there is a so-called over modulation (excess modulation). Simple demodulators (such as a quadratic detector) demodulate such a signal with strong distortions.

Bibliography:

• https://en.wikipedia.org/wiki/Amplitude_modulation